Zap-Stop
Al Thomason
All,
Hope this Email finds folks well. This week I was contacted by someone with a FET overtemp hard fault, upon more investigation it turned out the field drive FETs had failed, causing the overtemp.
In the cases I have been able to directly examine, these types of failures have been caused universally by unsuppressed voltage spikes on the +12v (or +24v) feed. Well known, and one of the defined ‘issues’ by SAE in transportation – the common approach to snubbing these spikes are through the use of avalanche diodes in the alternator.
And there is the rub,
It seems some aftermarket / rebuilt alternators do not use avalanche diodes, instead using lower-cost (and perhaps slightly more efficient) standard diodes in their rectifier pack. Leaving the system unprotected.
Though we have taken steps in the WS500 offering to mitigate this (And yes, this is part of the learning’s I got from the technology transfer from Michal Frost), I wanted to send this Email out to VSR folks and suggest a good protection might be to add one of the old ‘Zap Stop’ devices to their alternators, if there is any question. (The way to tell is place a storage O’Scope on the system for a period of time and run all the devices aboard. Looking for voltage spikes just a few mS long)
The issue with these spikes is they “appear” to come randomly. And depending on the vessel can occur within weeks, or maybe a couple of years after install. All depends on phase of moon, tides, what you named your 1st born, and a few other ‘dark’ conditions. (Actually, related largely to inductive loads being turned off such as: DC Refrigerators, windlass, even the alternator its self)
If you have any concern, I would suggest adding a Zap Stop type device to your alternators. The old Zap Stop is fine. Purchasing a TVS diode such as the MR2535L used in the old Zap_Stop, or perhaps this device would work well.
Really, and TVS device rated with a working voltage of around 20-24v (dbl for 24v deployments) and say a 400A or larger peak amperage help a lot. Install these AT the VSR Regulator between the ALT+ and ALT- terminals with the banded end towards the ALT+ side. Those with the Gen 3B reg: I have already soldered on a TVS diode on the bottom – but if you have a prior regulator, consider adding a TVS diode. (In fact, I have a stash of these I used on the 3B regulator – if you are in the US just drop me an Email and I will pop one into the mail. Make sure to tell me if this is 12v, 24v or 48v deployment)
Some commercial offerings would include:
https://shop.marinehowto.com/products/sterling-power-12v-transient-voltage-protection-device
https://www.westmarine.com/buy/balmar--alternator-spike-protector--7434293
Install those at the alternator.
-al-
Viking Star
45' Monk Sr. / McQueen